U.S. patent number 8,206,119 [Application Number 12/366,486] was granted by the patent office on 2012-06-26 for turbine coverplate systems.
This patent grant is currently assigned to General Electric Company. Invention is credited to Christopher Sean Bowes, John Wesley Harris, Jr., Gary Charles Liotta.
United States Patent |
8,206,119 |
Liotta , et al. |
June 26, 2012 |
Turbine coverplate systems
Abstract
In one embodiment, a coverplate may be configured to axially
overlay a plurality of blade retaining slots within a wheel post of
a rotor wheel. The coverplate may include a tab for radially
securing the coverplate within a complementary groove of the rotor
wheel and an aperture configured to align with a corresponding
aperture of the turbine wheel to receive a fastener for axially
securing the coverplate to the rotor wheel.
Inventors: |
Liotta; Gary Charles
(Simpsonville, SC), Bowes; Christopher Sean (Simpsonville,
SC), Harris, Jr.; John Wesley (Taylors, SC) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
42232717 |
Appl.
No.: |
12/366,486 |
Filed: |
February 5, 2009 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20100196164 A1 |
Aug 5, 2010 |
|
Current U.S.
Class: |
416/220R |
Current CPC
Class: |
F01D
11/005 (20130101); F01D 5/3015 (20130101); F05D
2240/55 (20130101); Y02T 50/60 (20130101); Y02T
50/671 (20130101) |
Current International
Class: |
F01D
5/32 (20060101) |
Field of
Search: |
;416/115,207,212R,219R,204R,220R,244A ;415/115 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ham; Seungsook
Attorney, Agent or Firm: Fletcher Yoder, P.C.
Claims
The invention claimed is:
1. A system, comprising: a coverplate configured to axially overlay
a plurality of blade retaining slots within a wheel post of a rotor
wheel, the coverplate comprising: a tab configured to couple to a
complementary groove to radially secure the coverplate to the rotor
wheel; an aperture configured to align with a corresponding
aperture of the rotor wheel to receive a fastener configured to
axially secure the coverplate to the rotor wheel; a sealing surface
configured to be disposed against the wheel post; a raised sealing
section disposed on the sealing surface, wherein the raised sealing
section encircles a perimeter of the coverplate and is configured
to interface with the wheel post to entirely encircle at least one
of the blade retaining slots; and a protrusion configured to
axially retain the coverplate within a complementary groove of a
blade extending from the wheel post.
2. The system of claim 1, wherein the aperture is disposed on a
peripheral flange of the coverplate, and wherein the peripheral
flange is configured to overlay a corresponding flange of the rotor
wheel.
3. The system of claim 1, wherein the tab extends from the sealing
surface of the coverplate.
4. The system of claim 3, wherein the coverplate comprises one or
more ribs disposed on a surface opposite to the sealing surface and
configured to direct the coverplate toward the rotor wheel during
operation of the rotor wheel.
5. The system of claim 1, wherein the coverplate is configured to
be affixed to the rotor wheel with a single non-integral
fastener.
6. The system of claim 1, comprising a gas turbine engine, a
compressor, a gas turbine, a combustor, or combinations
thereof.
7. A system, comprising: a coverplate configured to axially overlay
a plurality of blade retaining slots within a wheel post of a rotor
wheel, the coverplate comprising: a sealing surface configured to
be disposed against the wheel post; a raised sealing section
disposed on the sealing surface, wherein the raised sealing section
encircles a perimeter of the coverplate and is configured to
interface with the wheel post to entirely encircle at least one of
the blade retaining slots; and at least one recess disposed within
the sealing surface to reduce the area of the sealing surface that
contacts the wheel post.
8. The system of claim 7, wherein the coverplate comprises a
plurality of recesses disposed in the sealing surface and each
configured to overlay one of the plurality of blade retaining
slots.
9. The system of claim 7, comprising a second recess separated from
the at least one recess by a support bar, wherein the at least one
recess and the second recess are each configured to align with a
separate blade retaining slot of the plurality of blade retaining
slots, wherein the raised sealing surface is configured to encircle
the first recess and the second recess, and wherein the support bar
is recessed with respect to the raised sealing surface.
10. The system of claim 7, wherein the raised sealing surface is
configured to encircle at least two blade retaining slots.
11. A system comprising: a rotary machine comprising: a rotor wheel
comprising a wheel post with circumferentially spaced blade
retaining slots; a plurality of blades disposed within the blade
retaining slots to radially extend from the rotor wheel; and a
plurality of coverplates configured to axially overlay the blade
retaining slots, wherein at least one of the plurality of
coverplates comprises: a tab configured to radially secure the
coverplate within a complementary groove of the rotor wheel; an
aperture configured to align with a corresponding aperture of the
rotor wheel to receive a fastener configured to axially secure the
coverplate to the rotor wheel; a sealing surface configured to be
disposed against the wheel post; a raised sealing section disposed
on the sealing surface, wherein the raised sealing section
encircles a perimeter of the coverplate and is configured to
interface with the wheel post to entirely encircle at least one of
the blade retaining slots; and at least one recess disposed within
the sealing surface to reduce the area of the sealing surface that
contacts the wheel post.
12. The system of claim 11, wherein the rotary machine comprises a
gas turbine engine or a compressor.
13. The system of claim 11, wherein the plurality of coverplates
comprises a series of circumferentially adjacent coverplates each
disposed over at least two blade retaining slots and wherein the at
least one coverplate comprises a first recess and a second recess
disposed in the sealing surface, separated from one another by a
support bar, and encircled by the raised sealing section, and
wherein the support bar is recessed with respect to the raised
sealing surface.
14. The system of claim 11, wherein the plurality of coverplates
are disposed perpendicular to the plurality of blades.
15. The system of claim 11, wherein the at least one coverplate
comprises at least two parallel ribs disposed on a surface opposite
to the sealing surface and configured to direct the coverplate
toward the rotor wheel during operation of the rotor wheel.
16. The system of claim 11, comprising a bolt fastened through the
aperture of the coverplate and the corresponding aperture of the
rotor wheel.
17. The system of claim 11, wherein the at least one of the
plurality of coverplates comprises a protrusion configured to
axially retain the coverplate within a complementary groove of a
blade of the plurality of blades, wherein the blade extends from
one of the encircled blade retaining slots, and wherein the
aperture is disposed within a flange of the coverplate extending in
a direction opposite to the protrusion.
18. The system of claim 11, comprising a gas turbine engine, a
compressor, a gas turbine, a combustor, or combinations
thereof.
19. The system of claim 17, wherein the blade comprises a flange
that extends outwardly from the blade to form the complementary
groove.
20. The system of claim 1, wherein the coverplate comprises a first
recess and a second recess disposed in the sealing surface,
separated from one another by a support bar, and encircled by the
raised sealing section, and wherein the support bar is recessed
with respect to the raised sealing surface.
Description
BACKGROUND OF THE INVENTION
The subject matter disclosed herein relates to gas turbine engines,
and more specifically, to coverplates for turbines.
In general, gas turbine engines combust a mixture of compressed air
and fuel to produce hot combustion gases. The combustion gases may
flow through one or more turbine stages to generate power for a
load and/or a compressor. A pressure drop may occur between stages,
which may promote flow of a fluid, such as bucket or blade cooling
air, through unintended paths. Coverplates may be disposed over
turbine wheel posts to reduce fluid leakage between stages.
BRIEF DESCRIPTION OF THE INVENTION
Certain embodiments commensurate in scope with the originally
claimed invention are summarized below. These embodiments are not
intended to limit the scope of the claimed invention, but rather
these embodiments are intended only to provide a brief summary of
possible forms of the invention. Indeed, the invention may
encompass a variety of forms that may be similar to or different
from the embodiments set forth below.
In a first embodiment, a system includes a coverplate configured to
axially overlay a plurality of blade retaining slots within a wheel
post of a rotor wheel. The coverplate includes a tab configured to
couple to a complementary groove to radially secure the coverplate
to the rotor wheel. The coverplate also includes an aperture
configured to align with a corresponding aperture of the rotor
wheel to receive a fastener configured to axially secure the
coverplate to the rotor wheel.
In a second embodiment, a system includes a coverplate configured
to axially overlay a plurality of blade retaining slots within a
wheel post of a rotor wheel. The coverplate includes a sealing
surface disposed around the perimeter of the coverplate and
configured to interface with the wheel post to encircle at least
one of the blade retaining slots. The coverplate also includes at
least one recess disposed within the sealing surface to reduce the
area of the sealing surface that contacts the wheel post.
In a third embodiment, a system includes a rotary machine with a
rotor wheel that includes a wheel post with circumferentially
spaced blade retaining slots. The rotary machine also includes a
plurality of blades disposed within the blade retaining slots to
radially extend from the rotor wheel and a plurality of coverplates
configured to axially overlay the blade retaining slots. At least
one of the plurality of coverplates includes a tab configured to
radially secure the coverplate within a complementary groove of the
rotor wheel, an aperture configured to align with a corresponding
aperture of the turbine wheel to receive a fastener configured to
axially secure the coverplate to the rotor wheel, a sealing surface
disposed around a perimeter of the coverplate and configured to
interface with the wheel post to encircle at least one of the blade
retaining slots, and at least one recess disposed within the
sealing surface to reduce the area of the sealing surface that
contacts the wheel post.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in
which like characters represent like parts throughout the drawings,
wherein:
FIG. 1 is a schematic flow diagram of an embodiment of a gas
turbine engine that may employ turbine coverplates;
FIG. 2 is a sectional view of the gas turbine engine of FIG. 1
sectioned through the longitudinal axis;
FIG. 3 is a perspective view of a portion of the gas turbine engine
of FIG. 2 depicting an embodiment of a coverplate attached to a
turbine rotor;
FIG. 4 is a detail side view of the rotor of FIG. 3; and
FIG. 5 is a perspective view of the coverplate of FIG. 3 depicting
the sealing surface.
DETAILED DESCRIPTION OF THE INVENTION
One or more specific embodiments of the present invention will be
described below. In an effort to provide a concise description of
these embodiments, not all features of an actual implementation may
be described in the specification. It should be appreciated that in
the development of any such actual implementation, as in any
engineering or design project, numerous implementation-specific
decisions must be made to achieve the developers' specific goals,
such as compliance with system-related and business-related
constraints, which may vary from one implementation to another.
Moreover, it should be appreciated that such a development effort
might be complex and time consuming, but would nevertheless be a
routine undertaking of design, fabrication, and manufacture for
those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended
to mean that there are one or more of the elements. The terms
"comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements.
The present disclosure is directed to turbines that include
segmented coverplates with cross sections designed to transfer a
radial load from the coverplate into the rotor wheels to enhance
sealing. The coverplates may be disposed across two or more wheel
post openings to reduce the leakage of a fluid, such as turbine
blade cooling air, through the wheel posts and/or to reduce the
leakage of the fluid into the wheel space cavities. The coverplates
include raised sealing surfaces that interface with the wheel
posts. The sealing surfaces may have a relatively small area in
order to provide increased sealing force against the wheel posts.
Ribs may be disposed on a surface opposite to the sealing surface
to extend outward away from the wheel posts. The ribs may produce
torque during operation, thereby forcing the coverplate towards the
wheel to enhance sealing.
The coverplates are segmented to span one or more wheel post
openings, instead of a 360 degree coverplate that spans all of the
wheel post openings within a single rotor wheel. The segmented
design may allow field replacement of a coverplate without
disassembly of the rotor wheel. The segmented design also may allow
the coverplates to be constructed of materials capable of
withstanding higher temperatures since the segmented coverplates
may be exposed to lower tangential stresses than those applied to
the 360-degree coverplates. In certain embodiments, the higher
temperature materials may act as a heat shield to shield the rotor
wheel from the relatively hot wheelspace temperatures. The
coverplates may be affixed to the wheel posts by aligning a tab on
the coverplates with a corresponding groove on the wheel posts and
by inserting a fastener through corresponding apertures on the
coverplates and wheel posts. The tab may transfer loads into the
wheel to alleviate stress on the fastener during operation. In
certain embodiments, a protruding portion of the coverplates may be
inserted within a groove of the turbine blades to provide further
axial retention for the coverplate, or axial retention for the
turbine blade.
FIG. 1 is a block diagram of an exemplary system 10 including a gas
turbine engine 12 that may employ segmented coverplates with
enhanced sealing features. In certain embodiments, the system 10
may include an aircraft, a watercraft, a locomotive, a power
generation system, or combinations thereof. The illustrated gas
turbine engine 12 includes an air intake section 16, a compressor
18, a combustor section 20, a turbine 22, and an exhaust section
24. The turbine 22 is drivingly coupled to the compressor 18 via a
shaft 26.
As indicated by the arrows, air may enter the gas turbine engine 12
through the intake section 16 and flow into the compressor 18,
which compresses the air prior to entry into the combustor section
20. The illustrated combustor section 20 includes a combustor
housing 28 disposed concentrically or annularly about the shaft 26
between the compressor 18 and the turbine 22. The compressed air
from the compressor 18 enters combustors 29 where the compressed
air may mix and combust with fuel within the combustors 29 to drive
the turbine 22.
From the combustor section 20, the hot combustion gases flow
through the turbine 22, driving the compressor 18 via the shaft 26.
For example, the combustion gases may apply motive forces to
turbine rotor blades within the turbine 22 to rotate the shaft 26.
After flowing through the turbine 22, the hot combustion gases may
exit the gas turbine engine 12 through the exhaust section 24.
FIG. 2 is a side view of an embodiment of the gas turbine engine 12
of FIG. 1 taken along the longitudinal axis 30. As depicted, the
gas turbine 22 includes three separate turbine rotors 31. Each
rotor 31 may generally represent a stage within the turbine 22.
Each rotor 31 may include a set of blades 32 coupled to a rotor
wheel 34 that may be rotatably attached to the shaft 26 (FIG. 1).
The blades 32 may extend radially outward from wheel posts disposed
around the perimeter of the rotor wheels 34. The blades 32 may be
partially disposed within the path of the hot combustion gases.
Coverplates may be disposed over the wheel posts to prevent the
leakage of turbine blade cooling air through the wheel posts and/or
into the spaces between the rotor wheels 34. In certain
embodiments, reduction of cooling air leakage may improve turbine
efficiency. The coverplates may also act as a heat shield for the
rotor wheel and the wheel post. Although the gas turbine 22 is
illustrated as a three-stage turbine with three rotors 31, the
coverplates described herein may be employed in any suitable type
of turbine with any number of stages and shafts. For example, the
coverplates may be included in a single stage gas turbine, in a
dual turbine system that includes a low-pressure turbine and a
high-pressure turbine, or in a steam turbine. Further, the
coverplates described herein may also be employed in a rotary
compressor, such as the compressor 18 illustrated in FIG. 1.
As described above with respect to FIG. 1, air may enter through
the air intake section 16 and be compressed by the compressor 18.
The compressed air from the compressor 18 may then be directed into
the combustor section 20 where the compressed air may be mixed with
fuel gas. The mixture of compressed air and fuel gas is generally
burned within the combustor section 20 to generate
high-temperature, high-pressure combustion gases, which may be used
to generate torque within the turbine 22. Specifically, the
combustion gases may apply motive forces to the blades to turn the
wheels 34. In certain embodiments, a pressure drop may occur at
each stage of the turbine, which may promote airflow through
unintended paths. For example, turbine blade cooling air may flow
into the cavities between the turbine wheels 34, which may place
thermal stresses on the turbine components. In certain embodiments,
the interstage volume may be cooled by discharge air bled from the
compressor. However, flow of hot combustion gases into the
interstage cavities may abate the cooling effects. Further, bucket
cooling air, blade cooling air, and/or wheelspace purge flow may
leak between the wheel posts, which may reduce the efficiency of
the gas turbine engine 12. Accordingly, the coverplates may be
disposed over the wheel posts to reduce the leakage of turbine
blade cooling air into the interstage cavities and to protect the
turbine from the relatively high temperature cavity air.
FIG. 3 is a perspective view of a portion of one of the rotors 31
shown in FIG. 2. For illustrative purposes, only a portion of the
rotor 31 is illustrated. However, each rotor 31 may generally
include a circular wheel 34 with blades 32 (FIG. 2) extending
radially outward (arrow 36) from the wheels 34. For clarity, the
blades 32 are not shown in FIG. 3. However, the blades 32 (FIG. 2)
may generally be inserted into and extend from openings or blade
retaining slots 38 spaced circumferentially (arrow 40) around the
wheel 34. In certain embodiments, approximately 60 to 92 blades may
be mounted and spaced circumferentially around (arrow 40) the
wheels 34 and a corresponding axis of rotation (not shown).
The blade retaining slots 38 are disposed in an upper portion of
the turbine wheel 34, generally referred to as the wheel post 42.
In certain embodiments, the blade retaining slots 38 may include
dovetails designed to interface with complementary dovetails on the
ends of the blades 32 (FIG. 2). The wheel posts 42 may generally
hold the blades 32 within the wheel 34. When the blades are
inserted within the slots 38, gaps may exist at interfaces between
the wheel post 42 and the blades 32. In certain embodiments, bucket
or blade cooling air or wheelspace purge flow may leak through
these gaps. Accordingly, a coverplate 44 is attached to a first
surface 46 of the wheel post 42. In certain embodiments, a similar
style coverplate may be attached to an opposite surface 48 of the
wheel post 42.
The coverplate 44 axially overlays (direction indicated by arrow
50) the blade retaining slots 38 within the wheel post 36. A series
of coverplates 44 may be circumferentially placed together, in the
direction indicated by arrow 40, to overlay each of the blade
retaining slots 38 circumferentially spaced about the wheel post
42. The series of adjacent coverplates 44 may make up an annular
shape.
As shown in FIG. 3, the coverplate 44 spans and encircles two
adjacent blade retaining slots 38 within the wheel post 42.
However, in other embodiments, the coverplates 44 may have a larger
or smaller circumferential length 52 to overlay any number of blade
retaining slots 38 using a single coverplate 44. For example, an
individual coverplate 44 may overlay approximately 1 to 100 blade
retaining slots 38, and all subranges therebetween. More
specifically, an individual coverplate 44 may overlay approximately
2 to 30 blade retaining slots 38, or even more specifically,
approximately 2 to 5 blade retaining slots 38. Moreover, in certain
embodiments, the coverplates 44 may include additional features
such as angel wings, and other balance and support features, such
as balance ribs.
The coverplate 44 may be affixed to the wheel 34 by a tab 54 that
fits within a corresponding groove 56 of the turbine wheel 34. In
certain embodiments, the tab 54 may extend partially or entirely
along the circumferential length 52 of the coverplate 44. In
embodiments where the tab 54 extends entirely along the
circumferential length 52, the tabs 54 of adjacent coverplates 44
may combine to form an annular shape. The tab 54 and groove 56 may
be coupled together to radially secure (direction 36) the
coverplate 44 to the wheel post 34. In other embodiments, the
positions of the tab 54 and the groove 56 may be reversed.
Specifically, a tab may be disposed on the rotor wheel 34 that is
configured to fit within a groove of the coverplate 44.
A flange 58 extends from the rotor wheel 34 and mates with a
corresponding flange 60 of the coverplate 44. The flange 60 may
extend from a lower periphery of the coverplate 44 and may have a
scalloped shape. However, in other embodiments, the shape and size
of the flange 60 may vary. Each flange 58 and 60 may include a
corresponding aperture 62 (shown in FIG. 4) that receives a
fastener, such as a bolt 64, to axially secure (in the direction
indicated by arrow 50) the coverplate 44 to the wheel 34. The bolt
64 may include a single non-integral fastener for securing the
coverplate 44 to the wheel 34. In certain embodiments, the bolt 64
may be replaced by other types of fasteners such as pins, clips,
and the like that are bolted, welded or otherwise attached to the
wheel 34. The fastener 64 may be removed while in the field to
allow replacement of a coverplate 44, and in certain embodiments,
the coverplate 44 may be replaced without disassembly of the
turbine wheel 34. In certain embodiments, the bolt 64 may be the
only non-integral fastener used to affix the coverplate 44 to the
rotor wheel 34.
During operation, centrifugal forces (direction 40) may direct the
coverplate 44 axially (direction 50) toward the wheel 34 to enhance
the sealing. Specifically, the coverplate 44 may include
circumferential ribs 66 and 68 that extend from an outward surface
70 of the coverplate 44. The ribs 66 and 68 may create torque
during operation, which in certain embodiments may provide an
overturning moment, to enhance sealing of the coverplate 44 to the
wheel 34. In certain embodiments, the ribs 66 and 68 may function
to direct the coverplate 44 toward the rotor 31 during operation of
the rotor 31. The ribs 66 and 68 may extend parallel to each other
across the circumferential length 52 of the coverplate 44. However,
in other embodiments, the ribs 66 and 68 may extend along a
different portion of the coverplate 44. Further, any number of ribs
of varying shapes, sizes, and lengths may be provided.
FIG. 4 is a side view of the rotor 31 shown in FIG. 3. The
coverplate is affixed to the wheel 34 by the bolt 64 that extends
through the aperture 62. As described above with respect to FIG. 3,
aperture 62 may be formed by aligning corresponding apertures on
the coverplate flange 60 and the rotor wheel flange 58. According
to certain embodiments, the bolt 64 may have a smaller diameter
than the aperture 62 to impede contact between the bolt 64 and the
edges of aperture 62 during operation, thereby reducing loads on
the bolt 64. The joint formed by the tab 54 and the groove 56 may
substantially impede or prevent the coverplate 44 from rotating
about the bolt 64. The joint formed by the tab 54 and the groove 56
also may direct radial loads (direction 36) into the turbine wheel
34, thereby alleviating stress on the bolt 64. In certain
embodiments, tight tolerances may exist on the upper radial portion
72 of the groove 56. Further, in other embodiments, the tolerances
between the tab 54 and the groove 56 may vary. For example, in
certain embodiments, a gap may exist between the tab 54 and a
bottom portion 73 of the groove 56 to facilitate assembly.
The coverplate 44 also may include axial (direction 50) retention
features. For example, the blade 32 may include a flange 74 that
extends outwardly from the blade 32 to form a groove 76 that may
receive a protruding portion 78 of the coverplate 44. The
complementary groove 76 and protrusion 78 may join to axially
retain (direction 50) the coverplate 44 during operation of the
rotor wheel 34. However, in certain embodiments, the protruding
portion 78 may be omitted. Further, in other embodiments, the
relative positions of the groove 76 and the protrusion 78 may be
switched. Specifically, the coverplate 44 may include a groove for
retaining a protrusion that extends from one of the blades 32.
FIG. 5 is a perspective view illustrating a sealing surface 80 of
the coverplate 44. The sealing surface 80 may be disposed against
the wheel post 42 (FIG. 4) and includes a raised section 82
extending around the perimeter of the coverplate 44. Specifically,
the raised portion 82 extends circumferentially from just above the
tab 54 to protrusion 78. A pair of recesses 84 and 86 may be
disposed within the sealing surface 80. The recesses 84 and 86 may
generally have a shallower depth than the raised portion 82 to
reduce the area of the sealing surface 80 that contacts the wheel
post 42 (FIG. 4). The recesses 84 and 86 further may reduce the
weight of the coverplate, thereby reducing the centrifugal load the
coverplate imparts into the turbine wheel. The reduced area of the
sealing surface 80 may allow the centrifugal force to be
concentrated toward the wheel 34 over a relatively small area to
enhance the sealing. Specifically, only the raised sections 82 of
the coverplate 44 may contact the wheel post 42. In certain
embodiments, only approximately 10, 20, 30, 40, 50, or 60 percent
of the sealing surface 80 may contact the wheel post 42. A support
bar 88 may separate the recesses 84 and 86. The support bar 88 may
be recessed with respect to the raised section 82, but may not be
as recessed as the recesses 84 and 86. In certain embodiments, the
support bar 88 may be omitted.
The coverplates 44 illustrated herein may include additional
features and/or modifications. For example, additional features,
such as angel wings and balance ribs may be included. In another
example, the sizes and shapes of apertures 62 may vary. In certain
embodiments, the flange 60 may extend across the entire
circumferential length 52 (FIG. 3) of the coverplate 44. Further,
any number of recesses 84 and 86 may be included. In certain
embodiments, each recess 84 or 86 may generally align with a blade
retaining slot 38 (FIG. 3). For example, a coverplate 44 designed
to cover three blade retaining slots 38 may include generally three
recesses 84 or 86. However, in other embodiments, each recess 84 or
86 may overlay multiple blade retaining slots 38.
This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in
the art to practice the invention, including making and using any
devices or systems and performing any incorporated methods. The
patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such
other examples are intended to be within the scope of the claims if
they have structural elements that do not differ from the literal
language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal languages
of the claims.
* * * * *